Brittle or serpent stars are marine invertebrates which inhabit both sandy and rocky areas on the sea bed. These nocturnal relatives of sea stars possess a spiny, hard skin and long, serpentlike arms. Brittle stars typically crawl very slowly across the reef in search of detritus and other decaying material, but are capable of moving with speed when disturbed. Brittle stars are found in oceans worldwide in a variety of habitats, including tidal pools, the soft sand between reef structures and deep water. The species which are found in deep water live on and around living sponges.
Physical parameters, such as the ocean itself, wave action and prevailing currents bring about various types of marine ecosystems, which include different habitats and populations of marine creatures. Brittle stars are purely marine invertebrates and are not found in estuarine environments or fresh water. Those species of brittle stars which feed on debris and detritus are found principally on soft sand, which they sift through in search of food items. Those brittle stars which feed on organisms in the water column are not as dependent on large expanses of sea sand.
Brittle stars are marine invertebrate animals and live in seawater. Saltwater affects the brittle star’s metabolism, as these invertebrates do no have any mechanisms for osmoregulation, and their body fluids remain the same salt concentration as the sea. Brittle stars can therefore not forage or live in adjoining habitats, such estuaries, which have a lower salinity than the ocean. Brittle stars also draw minerals, such as calcium, from the surrounding water which is incorporated into their hard skin.
Brittle stars have adapted to their specific marine habitat and are accustomed to live in water with high carbonate hardness. Hardness relates to the amount of minerals which are dissolved, including magnesium, calcium, zinc and iron. The main components of marine water, in which brittle stars are found, are magnesium and calcium. These physical properties of the brittle star’s habitat are very different from rivers and lakes in which freshwater invertebrates live, which have reduced levels of minerals and may be very soft and acidic.
Habitats Created by Invertebrates
Living corals form huge reef structures and thereby create habitats in which other marine creatures can live. Brittle stars are found in coral reef habitats around the world, where they feed on the huge variety of microscopic organisms which live in these environments. Coral reefs support a great variety of life form, and brittle stars are able to find adequate shelter and food items both in the water column and in the soft substrate.